A little. Without reading the Guardian piece, I wouldn't even guess that delivery notifications have anything in common with security properties.
In other words, the messages are secure only when there is a double checkmark, not just a single checkmark. How am I supposed to know that?!? I am not even sure what do the checkmarks mean.
Frankly, that's not a "backdoor", that's just a poorly thought out GUI (in my opinion), that might eventually lead to backdoors with an evil server.